<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      const user = {};
      // Object.defineProperty(user, 'username', {
      //   value: 'jack',
      // });
      // Object.defineProperty(user, 'age', {
      //   value: 20,
      // });
      Object.defineProperties(user, {
        username: {
          configurable:false,
          value: 'jack',
        },
        age: {
          writable:false,
          value: 20,
        },
      });
      console.log(user);
    </script>
  </body>
</html>
